Slender structure



March 23, 1965 YlAN-NIAN CHEN SLENDER STRUCTURE Filed May 1 1961 2Sheets-Sheet l Jn-venfor: Y/n/v-N/A/v CHE/V March 23, 1965 YlAN-NIANCHEN $474,539

SLENDER STRUCTURE 7 Filed May 1, 1961 2 Sheets-Sheet 2 Jnveniar:

United States Patent Ofilice 3,l?4,589 Patented Mar. 23, 1965 3,174,539SLENDER STRUCTURE Yian-Nian Chen, Winterthur, Switzerland, assignor toSulzer Freres, S.A., Winterthur, Switzerland, a corporation ofSwitzerland Filed May 1, 1961, Ser. No. 1%,772 Claims priority,application Switzerland, May 6, 1960, 5, 170/ 6d 9 Claims. (Cl. 18923)The invention relates to slender structures subjected to repeatedbending, such as, for example, chimneys, towers, masts and the like, andrelates more particularly to novel damping means for said structures.

Chimneys and other slender structures, in addition to withstanding thestatic loading caused by wind pressure in the plane of wind movement,also have to deal with those periodic forces which are produced by eddycavitation, and are operative transversely of the wind direction thuscausing the structure to oscillate. The oscillations produced becomecritical when the firequency of eddy cavitations reaches the naturalfrequency or" the structure. In masonry chimneys and riveted metal platechimneys the internal damping is usually of sufiicient magnitude so thatthe oscillatory energy of relatively small oscillatory amplitudes isreadily absorbed. However, this is generally not the case with Weldedsheet metal chimneys. These structures require special measures toensure that dangerous resonance cannot occur. The known means ofachieving this object are to alter the natural frequency of the chimneyand also to release the strain by bracing the chimney with wire ropes.The disadvantage of varying the natural frequency of the chimney is thatchimney size and design often cannot be the most suitable for theparticular purpose required and, for instance, uneconomically largethicknesses of sheet must be used just to alter the natural frequency.Where dangerous oscillations occur in existing chimneys, the methodcannot be used at all. The second method -bracing by wire ropes-isexpensive and is aesthetically unsatisfactory. Accordingly, it is animportant object of this invention to provide means to reduce theoscillations of structures of the foregoing type without incurring thedisadvantages inherent in the known expedients, said means comprising atleast one dynamic oscillation damper. Other objects will appear from thefollowing detailed description.

The invention will be described with reference to embodimentsillustrated in the drawings wherein:

FIG. 1 illustrates a chimney according to the invention incorporating anoscillation damper of this invention.

FIG. 2 is a section through the damper shown in FIG. 1 on a somewhatenlarged scale.

FIG. 3 is a plan view of the damper mass shown in FIG. 2.

FIG. 4 is a side elevation showing the articulation of the severalelements comprising the damper mass shown in FIG. 2.

FIG. 5 is a section through another embodiment of the oscillation damperof this invention.

FIG. 6 illustrates a detail of FIG. 5.

FIGS. 7-12 are sectional views of other embodiments of the oscillationdampers of this invention.

Referring to FIG. 1, the chimney 1 made of steel plate carries theoscillation damper structure 2 at its top end. FIG. 2 is a sectionalview of the oscillation damper structure 2 and also includes the top endof the chimney. The chimney 1 comprises an outer generated surface 10and a lining 11 with heat insulation 12 being therebetween. The surfaceIt) bears brackets 13 to which an annular base plate 14 is secured. Thedamper structure is closed externally by an outer cylindrical cover 15.A ring 16 which constitutes the damping mass rests freely on the plate14 and this ring includes buffer elements 17 and 18. The buffer elements17 and 18 are disposed in bores 20 extending radially of the ring 16 andare normally pressed apart from one another by a spring 19. The bores 20are closed by cover plates 21 and the whole damper assembly is protectedagainst weathering by a cover plate 22. When the chimney starts tooscillate, for instance, because of eddy cavitation caused by wind, thedamping mass 16 starts to slide on the base 14 once the oscillationexceeds a critical amplitude, the amount of energy being absorbed beingequal to the product of the friction and the relative movement of themass. The function of the buffer element pins 17 and i8 is to keep thedamping mass at a distance from the closing walls as well as tointercept any impact of the damping mass against such walls.Conveniently, to ensure very uniform distribution of the friction forcesover the periphery of the damping mass, the mass is articulated, as canbe seen in FIGS. 3 and 4, by being formed from various sections 24interconnected by means of pins 26 loosely fitting in apertures 25. Thevarious sections 24 can move relatively to one another vertically andeach section 24 engages and rests upon the base 14 by its own weightonly. FIG. 3 illustrates an alternative method for the radial springingof the damping mass, using instead of the radial spring-loaded bufferelements 17 and 18, flat spring strips 27 which are secured by screws 28to the associated sections 24. In the oscillation damper shown in FIG.2, the base does not completely close the chamber surrounding thedamping mass, gaps 29 being left through which abraded particles candrop.

Another embodiment of the oscillation damper of this invention is shownin FIG. 5. in this case the damping mass takes the form of a rigid ring31 over which short ring segmental damping elements 32, which are of U-shaped cross-section, are loosely placed. The base over which thedamping mass slides is in the form of an open grating 33. To prevent thedamping mass from jamming, the damping elements 32 are formed withbevelled edges 35. In this embodiment the damping elements are preventedfrom striking the outer wall by the use of corrugated steel strips 34(FIG. 6).

FIG. 7 illustrates an oscillation damper in which damping is provided bymechanical friction and by liquid friction. Disposed in a casing 40secured to the chimney is an annular damping member 41; the innerchamber of the casing all is filled either Wholly or partly with aliquid, such as oil. When the damping mass 41 and the casing 4t moverelatively to one another as the chimney oscillates, hydraulic forcesare produced by the liquid filling, and not just mechanical friction asin the example hereinbefore described, the hydraulic forces thus createdhelping to dampen the oscillatory motion. Advantageously, the dampingelement 41 is formed at top and bottom with recesses 42 which reduce thecontact surface of the casing, thus ensuring that, if the oil in thecasing 49 becomes gummy, the adhesion between the element 41 and thecasing remains low.

FIG. 8 illustrates an oscillation damper operating purely by liquidfriction. An annular vessel 50 secured to the outer chimney surface 10comprises radial perforate metal plates 51, and the sectors bounded bythe plates 51 are filled with a porous loose fill, such as steel swarf.The vessel 50 is about half filled with a liquid forming the dampingmass. As liquid there is used preferably an oil having a fiatviscosity-temperature pattern and a low coagulation point, such assilicone oil. The advantage of the embodiment shown in FIG. 8 is thatdamping is provided at very reduced oscillations. The liquid in thevessel can be loaded with suspended particles; if required, relativelycoarse and non-suspendable particles, such as sand, stones, metal scrapand so on, can be added to the liquid and can move together therewith asthe chimney oscillates. If such a filling is used in the vessel 50, theplates 51 and the porous loose fill can be omitted.

Referring to the embodiment shown in FIG. 9, the oscillation damper isdevoid of any special damping mass; instead, some of the chimney is usedas damping mass. As a rule, in chimneys consisting of an outer coveringand a lining, the natural frequency of the outer covering is differentfrom and usually higher than the natural frequency of the chimney liningwhich is loaded with the insulation layer. In the embodiment shown inFIG. 9, sheet metal rings 51 are welded into the outer chimney surfaceIt), and the chimney lining bears against the rings 61, with reducedclearance, by way of sheet metal rings 62. As the chimney oscillates,there is friction between the rings 61 and 62 so that oscillationdamping is provided. The chimney lining 11 together with the insulationlayer 12 is used as damping mass for the other part.

FIG. illustrates a variant of the damper shown in FIG. 9. Referring toFIG. 10, brackets 70 are secured to the lining 11, and a number ofalternately arranged rings 71, 72 rest on the brackets 70. The rings 71have reduced clearance relatively to the lining 11 and considerableclearance relatively to the chimney outer surface 19. Conversely, therings 72 have reduced clearance relatively to the surface 10 andconsiderable clearance relatively to the lining 11. When the chimneyoscillates, the rings 71 move together with the lining 11, while therings 72 move together with the surface 10. There is, therefore,friction between the rings '71 and 72 so that oscillation of the chimneyis dampened.

Referring to FIG. ll, oscillation dampers 80 are secured to a chimneyouter surface. The dampers take the form of cylinders 81 in whichpistons 82 move freely. The cylinders 81 are wholly or partly filledwith a liquid, for instance, an oil. The cylinders 81 comprise springs83 which limit the movement of the pistons $2. When the chimney 10oscillates, the pistons 82 move relatively to the cylinders 81 becauseof their inertia; liquid flows through the gap between the piston andthe cylinder, leading to a friction which helps to dampen theoscillations. Of course, the piston 82 or the cylinder 81 can be formedwith ducts interconnecting the two chambers of each cylinder, and suchducts can be provided, in manner known per se, with valves or flapswhich inhibit or assist liquid flow in one or the other direction. Theadvantage of the dampers 80 shown in FIG. 11 is that they can be ofunitary construction and retained on bearings and can be provided to anyrequired number. Two dampers in which the damping mass in one dampermoves perpendicularly to the damping mass in the other can be used, inthe manner shown in FIG. 11, although more dampers can be used and canbe, for instance, uniformly distributed around the chimney axis.

FIG. 12 illustrates a variant of the damper shown in FIG. 11, the piston82 being replaced by a ball 83. This step helps to reduce veryconsiderably the possible disturbing mechanical friction between thecylinder 81 and the damping mass.

I claim:

1. In a relatively elongated vertical structure fixed at the lower endand free to oscillate at the upper end on being subjected to a bendingstress, the combination with the free upper end of said structure ofoscillation damping means, said damping means comprising a masssupported on and in mechanical and dry frictional engagement with thefree end of said structure, said mass being free to move relative tosaid structure when the latter oscillates from the vertical thereby toconvert at least part of the energy of said oscillation to drymechanical friction and effect the desired damping.

2. In a relatively elongated vertical structure fixed at the lower endand free to oscillate at the upper end on being subjected to a bendingstress, the combination with the free upper end of said structure ofoscillation damping means, said damping means comprising an annular masssupported on and in mechanical and dry frictional engagement with abracket integral with the free end of said structure, said annular massbeing free to move relative to said bracket and said structure when thelatter oscillates from the vertical thereby to convert at least part ofthe energy of said oscillation to dry mechanical friction and effect thedesired damping.

3. In a damped structure in accordance with claim 2, the combination ofspring-loaded impact means cooperating with said annular mass, saidimpact means being adapted to absorb the radially directed impact energyof said freely movable annular mass when coming in contact with theelongated structure on which it is supported as said structureoscillates.

4. A damped structure in accordance with claim 2 wherein the annularmass comprises a plurality of articu lated segments joined together.

5. In a relatively elongated structure comprising an inner shell and anouter shell which are fixed at one end and free to oscillate at theother end on being subjected to a bending stress, the combination withthe free end of said structure of oscillation damping means, saiddamping means comprising a first mass supported on the inside of theouter shell and another mass supported by said first mass, said mass esbeing in frictional engagement with but free to move relative to eachother when said structure oscillates thereby to convert at least part ofthe energy of said oscillation to friction and effect the desireddamping.

6. In an oblong structure comprising an inner shell and an outer shelland a space therebetween, said shells being fixed at one end and free tooscillate at the other end on being subjected to a bending stress, thecombination with the free end of said structure of oscillation damp ingmeans, said damping means being placed in said space and comprising:

a first mass supported by one of said shells,

a second mass resting on said first mass,

said means being in frictional engagement with but free to move relativeto each other when said structure oscillates thereby to convert at leastpart of the energy of said oscillation to friction and effect thedesired damping.

7. In an oblong structure as defined in claim 6 and wherein said firstmass is supported on the outside of the inner shell.

8. In an oblong structure as defined in claim 6 and wherein said massesare annular.

9. In anoblong structure comprising an inner shell and an outer shelland a space therebetween, said shells being fixed at one end and free tooscillate at the other end on being subjected to a bending stress, thecombination with the free end of said structure of oscillation dampingmeans, said damping means being placed in said space and comprising inalternating sequence the combination of at least one annular masssupported on the outto side of the inner shell and in peripheral contactwith the 5 6 inside of the outer shell and a second annular mass rest-References Cited in the file of this patent ing thereon whose inside isin peripheral contact with UNITED STATES PATENTS the outside of theinner shell, said masses being in frictional engagement with each otherbut free to move rela- 2,514,140 Connor I 3 1950 tive to each other whensaid structure oscillates from the 5 2,635,398 sllverman P 21, 1953vertical thereby to convert at least part of the energy of saidoscillation to friction and to effect the desired damp- FOREIGN PATENTSi 446,532 Canada Feb. 3, 1948

1. IN A RELATIVELY ELONGATED VERTICAL STRUCTURE FIXED AT THE LOWER ENDAND FREE TO OSCILLATE AT THE UPPER END ON BEING SUBJECTED TO A BENDINGSTRESS, THE COMBINATION WITH THE FREE UPPPER END OF SAID STRUCTURE OFOSCILLATION DAMPING MEANS,SAID DAMPING MEANS COMPRISING A MASS SUPPORTEDON AND IN MECHANICAL AND DRY FRICTIONAL ENGAGEMENT WITH THE FREE END OFSAID STRUCTURE, SAID MASS BEING FREE TO MOVE RELATIVE TO SAID STRUCTUREWHEN THE LATTER OSCILLATES FROM THE VERTICAL THEREBY TO CONVERT AT LEASTPART OF THE ENERGY OF SAID OSCILLATION TO DRY MECHANICAL FRICTION ANDEFFECT THE DESIRED DAMPING.